The invention relates to a component with a rear side contact and to a method for manufacturing same. Components of this type are used for example as sensors, actuators, active components, transistors, diodes, capacitors, resistors and the like, in particular for sensors which are resistant to high temperatures or to chemicals, radiation or magnetic fields. Actuators or sensors of this kind can be used in particular in the field of medical technology.
Conventionally, components of this type are contacted on the rear side by means of electrical through connection technology (via-hole technology). This technology is described for example in Heinz Beneking, Halbleiter Technologie (=semiconductor technology) B. G. Teubner-Verlag Stuttgart, 1991 and is used mainly in MMIC (Monolithic Microwave Integrated Circuits) technology. These are high-frequency ICs in which the rear side of the substrate represents an earth surface, i.e. the rear side of the IC is completely metallised. To the front side of the substrate are attached the components (resistors, transistors and the like), and additional non-sheathed cables. In order to realise an electrical earth connection of the components from the front to the rear side, through-holes are introduced into the substrate, the flanks of which holes are covered with metal. Thus the metallisation of the hole is accessible from the front side and from the rear side and can be connected on the front side to the components and on the rear side to the earth. What is disadvantageous about this is that not only is the rear side of the substrate partially coated with metal but also the function element itself consists of chemically reactive material. As a rule, the function element consists of an electronic or optoelectronic structure formed from semiconductor material such as GaAs. This semiconductor material is largely chemically reactive (and corrodes for example) and must be passivated (e.g. with SiO2 or Si3N4), which in turn makes very high demands of passivation technology.
Via-hole technology is therefore substantially limited to electronic/optoelectronic components.
The object of the present invention is to make available a component and a method for manufacturing same, which renders possible an electrical rear side contact whilst simultaneously preserving an inert component surface.
According to the invention, the component is produced by an electrically conductive layer being deposited on a substrate on the front side in the region of a future contact region and thereafter possibly additional layers being applied to form the function element. Then in the area of the contact region, the substrate is removed, starting from the rear side of the substrate, for example by a physical or chemical etching method, at least down to the electrically conductive layer and the recess so formed is metallised. Thus a component is produced which has no through-hole at the contact location and is consequently only metallised on the rear side. This renders possible a high radiological, chemical and physical resistance of the surface of the component since the metallic contact on the rear side is completely covered on the front side. Noble metal, base metal or even an alloy can therefore be used without taking into account the requirements made of the upper side of the component. Consequently an electrical rear side contact is produced whilst preserving the component surface. The physical, chemical and/or mechanical properties of the surface can therefore be completely exploited since the latter is freely available and not limited by metallised through-holes,. Thus additional diamond layers can also be applied to the surface of the component. With a complete diamond coating of the front side of the component, the excellent chemical, physical, electrical thermal and/or mechanical surface properties of the diamond can be exploited.
The electrically conductive layer can also be applied already as a conductive doped diamond layer, for example with a boron doping. The doping can here be designed in a variable manner in both vertical and horizontal directions, according to which component with the diamond coating is to be constructed on the front side of the substrate.
As the substrate can be used, for example, silicon, quartz, glass or even free-standing diamond. Non-doped diamond here has the advantages that it is completely non-conductive, such that it is possible to dispense with insulation between the diamond substrate and electrically conductive layers of the function element or of the contact metallisation. This saves further steps in the manufacturing process such that production is simplified overall. In this case the diamond substrate can also be produced as one piece with the function element, which can also be constructed from diamond layers.
Where silicon is used as the substrate it is necessary to insert an electrically insulating layer between the substrate and the electrically conductive layer of the function element and also between the substrate and the metallic rear side contact. This can be deposited for example as silicon oxide or silicon nitride or can be produced by oxidation of the silicon substrate to form silicon oxide.
Advantages about the use of diamond for the function element or for the complete coating of the front side of the component is in particular the fact that the diamond is resistant to high temperatures, completely non-conductive and chemically inert and has great hardness. Furthermore, a component with a diamond coating on the front side is suitable as a detector material for corpuscular radiation or high-energy X-rays since it is completely resistant to radiology. In particular it has no self-heating. The metal layers which are sensitive to radiation are then located protected merely on the rear side of the component.
The components according to the invention can be used as sensors, actuators, active components, transistors, diodes, capacitors, resistors and the like. As a result of their high stability they are particularly suitable as sensors, for example for pressure, impedance, temperature, in particular as sensors which are resistant to chemicals, corpuscular radiation, X-rays, high temperatures and/or magnetic fields. They can therefore be used in the field of medical technology, such as for example NMR tomography and also for instruments of micro-invasive surgery. There, for example, they can be used in catheters, which have to be completely sealed with respect to the human organism, in order to achieve high biomedical compatibility. This requires also the here guaranteed complete absence of chemically reactive elements such as e.g. metals on the catheter surface which comes into contact with the patient""s body.
By providing contact on both sides of the diamond layers by means of metallisation, in addition to the above-mentioned applications vertical structures and components such as e.g. back-gate transistors, photodiodes, photoconductors etc. can be realised. In addition, pn-diodes can be produced by epitaxial diamond layers with differing doping.
Diamond layers can be deposited and doped for example on silicon substrates over the entire surface in layer thicknesses of between several xcexcm and several mm. The deposition is usually carried out through the use of plasma-supported or hot wire methods. Selective depositions is here possible with the aid of SiO2 as the mask material. The layers so produced have, by comparison with natural diamonds, roughly identical mechanical, chemical and physical properties.
The removal of the substrate in the contact region can be effected by means of conventional etching methods. For example, dry or wet chemical etching or even physical etching is available for this purpose.
The definition of all the structures is achieved by means of known lithographic methods such as are usual in microsystem technology.
Some components are described by way of example in what follows.